Zhou Lepu, Lehan Nadine, Wehrenberg Uwe, Disteldorf Erik, von Lossow Richard, Mares Ute, Jarry Hubertus, Rune Gabriele M
Institute of Anatomy I, University Medical Center Hamburg-Eppendorf, Martinistr. 52, D-20246 Hamburg, Germany.
Exp Neurol. 2007 Jan;203(1):72-81. doi: 10.1016/j.expneurol.2006.07.020. Epub 2006 Sep 26.
Estrogen has been suggested to be pro-epileptic by reducing GABA synthesis, resulting in increased spine density and a decreased threshold for seizures in the hippocampus, which, once they occur, are characterized by a dramatic spine loss in the affected brain areas. As considerable amounts of estradiol are synthesized in the hippocampus, in this study we focused on aromatase, the rate-limiting enzyme in estrogen synthesis in order to examine the role of locally synthesized estrogens in epilepsy. To this end, we first examined the effects of letrozole, a potent aromatase inhibitor, on GABA metabolism in single interneurons of hippocampal dispersion cultures. Letrozole downregulated estradiol release into the medium, as well as glutamate decarboxylase (GAD) expression and GABA synthesis, and decreased the number of GAD positive cells in the cultures. Next, we counted spine synapses and measured estradiol release of hippocampal slice cultures, in which GABA(A) receptors had been blocked by bicuculline, in order to mimic epileptic activity. Treatment of slice cultures with bicuculline resulted in a dramatic decrease in the number of spine synapses and in a significant suppression of estrogen synthesis. The decrease in synapse number in response to bicuculline was restored by combined application of estradiol and bicuculline. Surprisingly, estradiol alone had no effect on either spine synapse number or on GAD expression and GABA synthesis. "Rescue" of synapse number in "epileptic slices" by estradiol and maintenance of GABA metabolism by hippocampus-derived estradiol points to a neuroprotective role of aromatase in epilepsy. Re-filling of estradiol stores after their depletion due to overexcitation may therefore add to therapeutical strategies in epilepsy.
雌激素被认为具有促癫痫作用，它通过减少γ-氨基丁酸（GABA）合成，导致海马体中的棘突密度增加和癫痫发作阈值降低，一旦癫痫发作，受影响脑区会出现显著的棘突丢失。由于海马体中会合成大量雌二醇，在本研究中，我们聚焦于芳香化酶，它是雌激素合成中的限速酶，目的是研究局部合成的雌激素在癫痫中的作用。为此，我们首先研究了强效芳香化酶抑制剂来曲唑对海马体分散培养的单个中间神经元中GABA代谢的影响。来曲唑下调了培养基中雌二醇的释放，以及谷氨酸脱羧酶（GAD）的表达和GABA合成，并减少了培养物中GAD阳性细胞的数量。接下来，我们对海马体脑片培养物中的棘突突触进行计数，并测量其雌二醇释放量，其中GABA(A)受体已被荷包牡丹碱阻断，以模拟癫痫活动。用荷包牡丹碱处理脑片培养物导致棘突突触数量急剧减少，并显著抑制雌激素合成。联合应用雌二醇和荷包牡丹碱可恢复荷包牡丹碱引起的突触数量减少。令人惊讶的是，单独使用雌二醇对棘突突触数量或GAD表达及GABA合成均无影响。雌二醇对“癫痫脑片”突触数量的“挽救”以及海马体衍生的雌二醇对GABA代谢的维持表明芳香化酶在癫痫中具有神经保护作用。因此，由于过度兴奋导致雌二醇储备耗尽后进行补充，可能会为癫痫治疗策略增添新内容。
